1. Field of the Invention
The present invention relates to the method for fabricating thin film transistor display device that possesses the advantages of planarized surface on the pixel region, simplified fabrication process and enhanced production yield.
2. Description of Related Arts
The transfer fabrication process enables thin film devices to be created on substrates which would otherwise be impossible with the present semiconductor fabrication technique. A thin film transistor display device is fabricated through a transfer process, which claims to possess good device performance after transferring a semiconductor component onto a plastic substrate.
With reference to FIGS. 12Axcx9cF, a semiconductor component is fabricated through a series of steps: providing a first transfer substrate (50); forming a sacrificial layer (501) on top of the first transfer substrate (50); forming a thermal insulation layer (51) over the sacrificial layer (501); forming a semiconductor film (52) over the thermal insulation layer (51); forming a first dielectric layer (53) over the semiconductor film (52); forming a gate electrode layer (56) over the first dielectric layer (53), thus completing the fabrication of a semiconductor component on the first substrate (50).
Afterwards, the semiconductor component is integrated with a transparent electrode layer to form an integrated driver circuit through a series of steps: forming a second dielectric layer (54) over the semiconductor component; forming a first passivation layer (55) over the second dielectric layer (54); forming a transparent electrode layer (57) on top the first passivation layer (55), where the transparent electrode (57) is connected to the semiconductor component after patterning as shown in FIG. 12A; forming a second passivation layer (60) over the first passivation layer (55) and the transparent electrode (57); bonding a supporting substrate (61) onto the second passivation layer (60) as shown in FIG. 12B.
Then, a second substrate (70) is glued on top of the semiconductor component, as shown in FIG. 12E, for transferring the semiconductor component from the first substrate (50) to the second substrate (70); heat is applied on the sacrificial layer (501) through laser irradiation to cause the sacrificial layer (501) to crack when an hydrogen explosion occurs on the inner surface of the first substrate (50) and the semiconductor component will detach from the surface of the first substrate (50) as shown in FIGS. 12 C and D (Since the sacrificial layer (501) is made with non-crystalline silicon film carrying hydrogen atoms, the laser beam creates thermal heat raising the internal temperature, and causes a hydrogen explosion in the thermal process); finally, the supporting substrate (61) and the second passivation layer (60) are removed to expose the transparent electrode (57) as shown in FIG. 12F.
The above process involves pre-forming of the semiconductor component over the first transfer substrate (50) and then transferring the semiconductor component from the first substrate (50) onto the second substrate (70) through a thermal process. The semiconductor component to be created on the first substrate can be thin film transistor (TFT), metal oxide semiconductor (MOS), metal insulator metal capacitor (MIM) or thin film diode (TFD). However, the above fabrication process still has several shortcomings:
Too many transfer substrates: from the formation of the semiconductor component to the successful transfer of the semiconductor component onto the final substrate, at least three transfer substrates are needed.
Complex process and high process costs: using so many substrates in the process also entails complex processing steps, and furthermore the support substrate and the temporary protective layer will be discarded after one-time use in the thermal process. The above process is only part of the complete process which should further include the steps of forming the optical component and aligning the semiconductor component and the optical component.
Raised surface on the pixel electrode: since the pixel electrodes are formed under high temperature, the raised surface layer will cause uncontrolled electric discharge at the pointed edges resulting in abnormal white points on the display screen.
The fabrication process for thin film transistor display devices can be further improved to simplify the process and lower the process costs.
The main object of the present invention is to provide a method for fabricating thin film transistor display device by an economical means, whereby an integrated driver circuit with both the semiconductor component and the optical component can be successfully transferred from a first substrate onto a second substrate through a one-time thermal process, without degradation of device performance and consuming no substrates in the process. Since the semiconductor component and the optical component are formed and integrated on the first substrate before the transfer process, there is no need of further alignment. Also, the fully planarized surface of the pixel electrode can enhance the quality of display image.
The fabricating process comprises the steps of:
forming a pixel electrode directly over the sacrificial layer of the first substrate;
forming a semiconductor component on top of the pixel electrode layer;
performing testing on the semiconductor component to confirm the electrical characteristics;
forming an optical component, where the materials can be color conversion materials, filtering lens, polarizing film, light enhancing film, diffusion film, angle focusing film, wide angle lens, anti-reflection and reflection film, light absorption film, or a combination of the above, over the semiconductor component, thus forming an integrated driver circuit made up of a semiconductor component and an optical component on the same surface of the first substrate;
providing a second substrate for gluing onto the optical component on the first substrate;
applying heat on the back side of the first substrate to cause the surface of the sacrificial layer to crack and the semiconductor component and optical component to detach from the first substrate in a thermal process; and
etching away the pixel electrode originally formed on the first substrate to expose the pixel region, thus completing the fabrication of the thin film transistor display device.
Since the semiconductor component and the optical component are fully integrated on the first substrate before the thermal process, there is no need of further alignment of the two components after successful transfer onto the second substrate. It can also be observed that the pixel region electrodes fully planarized to produce good display images. No protective layer and supporting substrate are used in the whole process, thus simplifying the fabrication and reducing the process costs.
The features and structure of the present invention will be more clearly understood when taken in conjunction with the accompanying drawings.